Installation

Tip: Stable releases are even-numbered (1.8, 1.10) while development releases are odd-numbered (1.9, 1.11). These development releases are available with lightdm-develAUR. Also available is lightdm-gitAUR.

Greeter

You will probably want to install a greeter. A greeter is a GUI that prompts the user for credentials, lets the user select a session, and so on. It is possible to use LightDM without a greeter, but only if an automatic login is configured; otherwise you will need to install xorg-server and one of the greeter packages below.

The official repositories contain the following greeters:

lightdm-gtk-greeter: this is the default greeter LightDM attempts to use when started unless configured to do otherwise.

You can set the default greeter by changing the [Seat:*] section of the LightDM configuration file, like so:

/etc/lightdm/lightdm.conf

[Seat:*]
...
greeter-session=lightdm-yourgreeter-greeter
...

One way to check which greeters are available is to list the files in the /usr/share/xgreeters directory; each .desktop file represents an available greeter. In this example, the lightdm-gtk-greeter and lightdm-kde-greeter greeters are available:

Enabling LightDM

Command line tool

LightDM offers a command line tool, dm-tool, which can be used to lock the current seat, switch sessions, etc, which is useful with 'minimalist' window managers and for testing. To see a list of available commands, execute:

$ dm-tool --help

User switching

The factual accuracy of this article or section is disputed.

Reason: Is this warning inappropriate? Don't dm-tool lock and dm-tool switch-to-greeter do the equivalent of calling loginctl lock-session? If your screen locker doesn't register with logind then there's nothing dm-tool ... can do - but that's not LightDM's fault. This issue is well known and touched upon here and here. (Discuss in Talk:LightDM#)

LightDM's dm-tool command can be used to allow multiple users to be logged in on separate ttys. The following will send a signal requesting that the current session be locked and then will initiate a switch to LightDM's greeter, allowing a new user to log in to the system.

X session wrapper

If you are migrating from xinit, you will notice that the display is not launched by your shell. This is because, as opposed to your shell starting the display (and the display inheriting the environment of your shell), LightDM starts your display and does not source your shell. LightDM launches the display by running a wrapper script and that finally exec's your graphic environment. By default, /etc/lightdm/Xsessions.conf is run.

Environment variables

The script checks and sources /etc/profile, ~/.profile, /etc/xprofile and ~/.xprofile, in that order. If you are using a shell that does not source any of these files, you can create an ~/.xprofile to do so. (In this example, the login shell is zsh)

If you have shell variables that are important for your display (such as Gtk or QT themes, GNUPG location, config overrides, etc.) this will let your graphic environment have access to your environment without having to be launched by your login shell.

Keymap

The script runs Xkbmap with arguments provided in files /etc/X11/Xkbmap, ~/.Xkbmap. If those files are not found, it runs xmodmap with /etc/X11/Xmodmap, ~/.Xmodmap. If using xkbmap, the files are parsed using cat. The following example works

Note: It is recommended to place the PNG or JPG file in /usr/share/pixmaps since the LightDM user needs read access to the wallpaper file.

GTK3 Theme

GTK3 themes can be specified with the theme-name variable in the [greeter] section of /etc/lightdm/lightdm-gtk-greeter.conf For example, theme-name=Adwaita-dark.

Webkit2 greeter

The lightdm-webkit2-greeter allows you to choose a background image directly on the login screen. It also offers an option to display a random image each time it starts if you use the Material theme. By default, images are sourced from /usr/share/backgrounds. You can change the background images directory by editing lightdm-webkit2-greeter.conf. For example:

/etc/lightdm/lightdm-webkit2-greeter.conf

[branding]
background_images = /usr/share/backgrounds

Note: The background images directory must be accessible to the LightDM user so it should not be located anywhere under /home.

Unity greeter

Users using the lightdm-unity-greeterAUR must edit the /usr/share/glib-2.0/schemas/com.canonical.unity-greeter.gschema.xml file and then execute:

Enabling autologin

Edit the LightDM configuration file and ensure these lines are uncommented and correctly configured:

/etc/lightdm/lightdm.conf

[Seat:*]
autologin-user=username

You must be part of the autologin group to be able to login automatically without entering your password:

# groupadd -r autologin
# gpasswd -a username autologin

LightDM logs in using the session specified in the ~/.dmrc of the user getting logged in automatically. To override this file, specify autologin-session in lightdm.conf:

/etc/lightdm/lightdm.conf

[Seat:*]
autologin-user=username
autologin-session=session

You will also need to ensure you have the accountsservice package installed, otherwise LightDM will fail to start, and running it from the command line will show Error getting user list from org.freedesktop.Accounts.

Note: GNOME users, and by extension any gnome-keyring user will have to set up a blank password to their keyring for it to be unlocked automatically.

Enabling interactive passwordless login

LightDM goes through PAM so you must configure the lightdm configuration of PAM:

You must then also be part of the nopasswdlogin group to be able to login interactively without entering your password:

# groupadd -r nopasswdlogin
# gpasswd -a username nopasswdlogin

Note: GNOME users, and by extension any gnome-keyring user may have to follow the instructions at the end of the previous section on enabling autologin.

To create a new user account that logs in automatically and additionally able to login again without a password the user can be created with supplementary membership of both groups, e.g.:

# useradd -mG autologin,nopasswdlogin -s /bin/bash username

Hiding system and services users

To prevent system users from showing-up in the login, install the optional dependency accountsservice, or add the user names to /etc/lightdm/users.conf under hidden-users. The first option has the advantage of not needing to update the list when more users are added or removed.

Default session

Adjusting the login window's position

GTK+ greeter

Users need to edit /etc/lightdm/lightdm-gtk-greeter.conf and enter a value for the position variable. It accepts x and y values, either absolute (in pixels) or relative (in percent). Each value can also have an additional anchor location for the window, start, center and end separated from the value by a comma.

Example:

position=200,start 50%,center

VNC Server

Lightdm can also be used to connect to via VNC. Make sure to install tigervnc on the server side and optionally as your VNC client on the client PC.

Setup an authentication password on the server as root:

# vncpasswd /etc/vncpasswd

Edit the LightDM configuration file as shown below. Note that listen-address configures the VNC to only listen to connections from localhost. This is used to only allow connections via SSH and port forwarding. On the SSH client, make sure that you use localhost:5900 for the tunnel destination; using 127.0.0.1:5900 or ::1:5900 is not reliable on dual stack network connections. If you want to allow insecure connections you can disable this setting.

Note: If you get a blank screen upon opening the VNC connection, try a different LightDM greeter.

Lock the screen using light-locker

light-locker is a simple screen locker using LightDM to authenticate the user. Once it is installed and running you can lock your session using

$ light-locker-command -l

This requires light-locker to be started at the beginning of your session - see Autostarting.

Troubleshooting

If you encounter consistent screen flashing and ultimately no LightDM on boot, ensure that you have defined the greeter correctly in LightDM's config file. And if you have correctly defined the GTK greeter, make sure the xsessions-directory (default: /usr/share/xsessions) exists and contains at least one .desktop file.

The same error can happen on lightdm startup if the last used session is not available anymore (eg. you last used gnome and then removed the gnome-session package): the easiest workaround is to temporarily restore the removed package. Another solution might be:

Wrong locale displayed

In case of your locale not being displayed correctly in Lightdm add your locale to /etc/environment

LANG=pt_PT.utf8

Alternatively if you want LightDM and its greeters to be in a language other than your set system locale, you can use the Environment= option in Systemd#Drop-in files.

Missing icons with GTK greeter

If you are using lightdm-gtk-greeter as a greeter and it shows placeholder images as icons, make sure valid icon themes and themes are installed and configured. Check the following file:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
theme-name=mate # this should be the name of a directory under /usr/share/themes/
icon-theme-name=mate # this should be the name of a fully featured icons set directory under /usr/share/icons/

LightDM freezes on login attempt

You may find that after entering the correct username and password and attempting to log in, LightDM freezes and you are unable to continue to the desktop. To fix the issue, reinstall the gdk-pixbuf2 package. See this forum thread.

LightDM displaying in wrong monitor

If you are using multiple monitors, LightDM may display in the wrong one (e.g. if your primary monitor is on the right). To force the LightDM login screen to display on a specific monitor, edit /etc/lightdm/lightdm.conf and change the display-setup-script parameter like this:

/etc/lightdm/lightdm.conf

display-setup-script=xrandr --output HDMI1 --primary

Replace HDMI1 with your real monitor ID, which you can find from xrandr command output.

Alternatively, if you are using the GTK+ greeter, you can edit /etc/lightdm/lightdm-gtk-greeter.conf and add the active-monitor parameter like this:

/etc/lightdm/lightdm-gtk-greeter.conf

[greeter]
active-monitor=0

Replace 0 with the desired display number.

LightDM does not appear or monitor only displays TTY output

It may happen that your system boots so fast that LightDM service is started before your graphics drivers are properly loaded. If this is your case, you will want to add the following config to your lightdm.conf file:

[LightDM]
logind-check-graphical=true

This setting will tell LightDM to wait until graphics devices are ready before spawning greeters/autostarting sessions on them.